Programmable logic controller modules ("PLC modules") can be used in a wide variety of applications. The versatility of the PLC modules results from their ability to be individually programmed and wired to perform different logic control functions and their modular construction which allows them to be inserted and removed from a system as needed. Each individual PLC module has a specified input, output, and coupling or control function.
The module is made from steel plates joined together to form a box. A printed circuit board, with all the circuits necessary to perform the module's specified function, is disposed in the box.
As shown in FIG. 1, a PLC module 3, or a series of such modules, are attached to a backplane 1. The pins of a bus connector 4 on the module 3 mate with holes in a bus connector 2 on the backplane 1 to create the electrical bus connection between the module and the backplane 1. Interfacing input/output wiring, a bus cable or other communication cable (not shown) leads from the front 8 of the module 3.
The PLC module 3 is attached to the backplane 1 by a hook 5. After the module 3 is hooked to the backplane 1, it swings, as illustrated by the arrow in FIG. 1, to mate the bus connectors 2 and 4. A screw 6 is the provided which extends through the lower part of the module 3 and screws into a threaded hole in the backplane 1. The hook 5 and screw 6 secure the module 3 to the backplane 1.
However, there is no lateral support and marginal vertical support for the module 3. Accordingly, if there are any vibrations or disturbances the module 3 may be caused to swing from side to side or lift vertically, and the pins of the bus connector 4 may be damaged. The result may be a faulty electrical connection between the module 3 and the backplane 1.
If the PLC module is exposed to an environment where disturbances or vibrations are common, this damage may be significant and recurring. These same vibrations, if unchecked, may also result in faulty operation of the modules electromechanical components, such as relays, by causing contact bounce.
Even if the PLC module is isolated from common physical disturbances, the eventuality of an earthquake may still damage the connection. While this would not normally be a risk worth considering, if the PLC module is used as part of the control or monitoring system for a nuclear power plant, it must function before, during and after any seismic disturbance to prevent the possibility of a nuclear accident. Such earthquake-proofing is mandated by law for nuclear power plants.
Accordingly, there is a need in the art for a device and method of supporting PLC modules mounted to a backplane to prevent lateral and vertical movement and consequent damage to the electrical connection between the modules and the backplane.